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| Titel |
Oxidation of the ocean crust: When does it happen? |
| VerfasserIn |
Jennifer Rutter, Michelle Harris, Damon Teagle, Rosalind Coggon, Jeff Alt, Christopher Smith-Duque |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250133164
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| Publikation (Nr.) |
 EGU/EGU2016-13742.pdf |
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| Zusammenfassung |
| Hydrothermal circulation on the ridge flanks is responsible for removing over two thirds of
the global hydrothermal heat flux and given the large volumes of fluids involved it has the
potential to impart significant geochemical signatures into the ocean crust and oceans.
Despite this global significance, two of the key parameters that will influence the heat and
geochemical fluxes of ridge flank circulation, the distribution and timing, are poorly
constrained. Ridge flank circulation is recorded by the ocean crust through the
formation of secondary hydrothermal minerals that form in response to seawater/rock
interaction. In the upper oceanic crust this alteration is characterised into secondary
minerals formed under either oxidising or reducing conditions, where oxidising
conditions suggest relatively open circulation and reducing conditions restricted
circulation. These prevailing conditions are intimately linked to fluid pathways and
their distribution in the crust and result in variations in the oxidation of the crust
from primary values. The oxidation state of whole rock samples combined with the
secondary minerals present therefore preserve a record of the prevailing conditions
of hydrothermal alteration and can be used to investigate ridge flank fluid/rock
reaction.
In this study we use new and literature whole rock Fe3+/FeTOT ratios from a global
sample set of ocean crust sampled by DSDP/ODP/IODP to investigate the timing and
distribution of oxidation of the ocean crust. This data set represents the most comprehensive
sampling of the ocean crust (0.3 – 170 Ma), and for each site accounts for variation in flow
types, alteration type and crustal depth, allowing robust estimates for the overall oxidation
state of each crustal site to be made and global trends to be deciphered. The vast majority of
the dataset has a range in oxidation state of 18-60% Fe3+/FeTOT, where 18% represents the
general pre-alteration value of the crust, indicating that nearly all samples have undergone
fluid/rock reaction and oxidation. The weighted mean oxidation state of the ocean
crust does not display a simple linear relationship with crustal age but instead is
established early and maintained throughout the progressive aging of the crust. Detailed
investigations of key sites demonstrate that although the mean oxidation state does not vary
with crustal age, the complexity of hydrothermal alteration does increase with age. |
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